1. Field of the Invention
The present invention relates to an optical semiconductor module used for an optical communication or transmission system, and in particular, to an optical guide holding member and an optical module having an improved electric wiring.
2. Description of the Related Art
In recent years, an optical transmission and communication techniques is developed and widely applied in various field, in which a light beam is utilized as a carrier and is intensity-modulated or phase-modulated to transmit signals. In such optical transmission and communication techniques, it is required to provide an optical coupling apparatus that optically couples a semiconductor device such as a light emitting or receiving element to optical guides such as optical fibers.
For this type of apparatus, a technique has been studied and developed which uses a coupling scheme called direct optical coupling (butt joint) to reduce implementation costs; this technique arranges a group of optical fibers and an optical semiconductor device immediately close to and opposite each other to achieve optical coupling without any lenses. The direct optical coupling requires the group of optical fibers and the semiconductor device to be arranged as close as several tens of μm to each other. Thus, for example, JP-A 2001-159724 (Kokai) proposes a method of producing electric wiring directly on a principal surface of an optical guide holding member (what is called an optical fiber ferrule) that holds optical fibers or the like and mounting an optical device on the principal surface so that a light sensitive region or an emitting region of the optical device is opposite the optical fibers.
This method enables the optical semiconductor device to be placed very close to the optical fibers. The optical semiconductor device can also be mounted on the optical guide holding member with respect to the optical fibers. This enables the optical semiconductor device to be precisely mounted also in a lateral direction by using a normal flip-chip implementation scheme. Nevertheless, the resulting structure has a reduced number of parts and allows costs to be readily reduced. Moreover, production costs can be sharply reduced by using resin as a base material for the holding member. When electric wiring is formed on a principle surface with openings for optical fibers and then extended to a side surface, an orthogonal arrangement is realized which enables an electric signal to be output in a direction orthogonal to a propagation path for the optical beam. This enables the optical fibers to extend parallel to a mounting surface of a mounting board, thus preventing the optical fibers from extending perpendicularly to the mounting surface.
In the optical module described in JP-A 2001-159724 (Kokai), it is required that the optical module is mounted on a mounting board so as to arrange the optical fibers parallel to the mounting surface of the mounting board. Thus, the electric wiring is required to be formed three-dimensionally on the principal surface of the optical guide holding member, on which the optical semiconductor device is mounted, and the electric wiring is also required to be extended from the principal surface to a side surface. Consequently, this structure has a disadvantage that the process of manufacturing electric wiring involves a three-dimensional process. This disadvantageously complicates the process and increases costs.
In the structure described in JP-A 2001-159724 (Kokai), the electric wiring is formed into an L-shape along an outer surface of the optical guide holding member and is electrically connected to a bonding wire on a side surface of the optical guide holding member. Consequently, a bonding operation exerts a strain on the base material of the optical guide holding member through electrode portions of the electric wiring. On the other hand, to inexpensively manufacture an optical guide holding member, resin can be effectively used as a base material and is adopted for many products. In this case, since the base material is resin, stress may strain the base material so that the base material caves in. This makes it difficult to achieve stable bonding, and in the worst case, the electrode parts may be strained and open-circuited.
According to an aspect of the present invention, there is provided an optical module comprising:
an optical guide;
a member having a first surface and a second surface adjacent to the first surface and a through hole having an opening on the first surface, the through hole being extended in the main body and the optical guide being held in the through hole;
electrical leads each having one and opposite ends, which are buried in the main body, have a part exposed on the first surface, and are arranged in the main body such that the opposite end of the electric lead being exposed on the second surface; and
an optical semiconductor device mounted on the first surface and having electrodes which are electrically connected to the exposed part of the electrical leads. In FIG. 1, reference numeral 1 denotes a member that holds optical guides, for example, optical fibers. The holding member 1 has a main body formed in a rectangular block having a principal surface, i.e., a mounting surface 8 and an opposite surface. Through holes 2 are formed in the main body and are arranged substantially parallel in the main body. The holding holes 2 are opened on a principal surface 8 and the opposite surface of the main body. The optical guides are inserted from the openings on the opposite surface into the through holes 2 so that the optical guides are held in the through holes 2, respectively. The holding member 1 also has electric leads 3 buried in the main body of the holding member 1 at the principal surface side. The openings 4 of the through holes 2 are arranged in line on the principal surface 8 and the end faces of the optical guides are positioned in the openings 4 on the principal surface 8 so that the end faces of the optical guides are arranged in line on the principal surface. The ends of the optical guides are exposed as optical input or output ports from the openings 4. An optical device is mounted on the mounting surface 8.
A drive element that drives the optical semiconductor device is connected, by bonding or the like, to the ends of wires 5 and 7 exposed from a side surface 32 of the optical guide holding member 1. The end of each wire 7 exposed from another side surface opposite the side surface 32 is connected to a mounting board 17 via bumps 20 (see FIG. 6). The electric leads 3, i.e., the signal wires 5 and common wires 7 are initially coupled together via tie bars 13. With a fine electrode pattern, the electrodes have a small width so that it is difficult to ensure the strength of the pattern. Thus, auxiliary tie bars 11 may be preferably provided on the lead frame 10 of fine electrode pattern so as to be close to the optical guide holding member 1 and the signal wires 5 and common wires 7 may be coupled together via the auxiliary tie bars 11 to ensure the strength of the pattern, as shown in FIG. 2. Reference numeral 12 denotes a positioning hole for the lead frame 10. The pattern for one optical guide holding member is shown in FIG. 2. However, in the lead frame 10, shown in FIG. 2, similar patterns are arranged above and below and coupled together, and another other optical guide holding members (not shown) may be also arranged in accordance with the patterns. on a side surface of the optical guide holding member. Consequently, a bonding operation exerts a strain on the base material of the optical guide holding member through electrode portions of the electric wiring. On the other hand, to inexpensively manufacture an optical guide holding member, resin can be effectively used as a base material and is adopted for many products. In this case, since the base material is resin, stress may strain the base material so that the base material caves in. This makes it difficult to achieve stable bonding, and in the worst case, the electrode parts may be strained and open-circuited.